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Spin-orbit coupling

Here, we make use of an ultrashort laser pulses to efficiently populate electronic states of Bi (111) up to 0.5 eV above the Fermi level. By these means, we show that the spin orbit splitting of surface states has a giant anisotropy with respect to the in-plane crystallographic axis. As show in the figure, the SO splitting is 150 meV along the G - M direction and increases by 250% for a rotation of 6° around the surface normal. In panel A and B the photons are polarized parallel and orthogonal to the G-M direction, respectively. We checked the SO anisotropy by first principle calculations of the band structure, finding excellent agreement with the observed dispersion of electronic states. The analysis of the resulting wave functions indicates that the SO anisotropy is due to the buckling of the spin orientation out of the surface plane. This spin polarization is important for possible technological applications, as it would affect the spin transport in nonballistic devices.

[1] Giant Anisotropy of Spin-Orbit Splitting at the Bismuth Surface; Y. Ohtsubo, J. Mauchain, J. Faure, E. Papalazarou, M. Marsi, P. Le Févre, F. Bertran, A. Taleb-Ibrahimi, and L. Perfetti, Phys. Rev. Lett. 108, 256808 (2012).